Events in Muscle fibre:
(i) A nerve impulse arriving at neuromuscular junction stimulates contractile response.
(ii) Due to the Depolarisation of the surface of sarcomeres, it spreads quickly.
(iii) Neurotransmitter is released at the neuromuscular junction.
(iv) It enters into the sarcomere through membrane channel. Na+ moves inside the sarcomere.
(v) It is called inflow of Na+ .
(vi) Action potential is generated in the sarcomere Action potential travels to the full length of muscle fibre.
(vii) The sarcoplasmic reticulum, then, releases the Ca++ which is stored here.
(viii) It binds to the specific sites found in the troponin of the thin actin filament.
(ix) Change takes place in troponin and active sites of F-actin are exposed to myosin head.
(x) Myosin head shows Mg++ dependent ATPase activity.
(xi) During relaxation of muscle, Ca++ is pumped back into the sarcoplasmic reticulum.
(xii) Consequently, the troponin component is freed to inhibit the active sites for myosin head. Cross bridges are broken.
(xiii) The thin filaments assume their normal position.
(xiv) The muscle fibre then comes in relaxed state.